The following abbreviations are used in the present specification:
CS circuit switched
eNB evolved Node B
GSM Global System for Mobile Communications
MAC media access control
NRT non-real-time
PS packet switched
RT real-time
SAR specific absorption rate
SIM subscriber identity module
TDMA Time Division Multiple Access
UE user equipment
WCDMA Wideband Code Division Multiple Access
A multi-SIM (subscriber identity module) wireless device, including particularly mobile devices such as mobile phones (including so-called “smart phones”), personal digital assistants, tablet and laptop computers, etc., can hold two or more SIM cards. Currently, such devices can typically hold two SIM cards, though phones that can hold three SIM cards are now available and it is likely that phones and other wireless devices that can hold more SIM cards will become available. For simplicity and brevity, reference will often be made in this specification to a dual-SIM device, which can operate with two networks and/or tariff arrangements, etc., but it will be understood that much of what is described herein can be applied to a multi SIM wireless device having in principle any number of SIMs for operating with a corresponding number of networks and/or tariff arrangements, etc.
Dual-SIM operation allows the use of two services without the need to carry two devices at the same time. For example, the same handset can be used for business and private use with separate numbers and bills. As another example, both SIMs may be used with the same network operator, for example to achieve a higher total bandwidth for data connections. As yet another example, the device may contain both cellular and non-cellular radios which are used for voice and data communication respectively using the different SIMs. In any event, using multiple SIMs allows the user to take advantage of different pricing plans for calls and text messages to certain destinations as well as mobile data usage, and/or to keep personal and business use separate for example, and/or to achieve higher bandwidth, and/or to obtain coverage across different networks using a single handset. The present invention is particularly concerned with mobile wireless devices that have two (or more) SIMs and radio systems which can be used simultaneously, and thus allow for example a user to send or receive data whilst making a voice call, and/or to have plural voice calls active simultaneously, and/or to have plural data calls active simultaneously, all on the one device and using the separate radio systems. The wireless devices may have cellular radio systems, non-cellular radio systems or both.
Wireless devices typically need to adjust the transmit power of their radio system(s) depending on the surrounding radio environment. As a particular example, in Wideband Code Division Multiple Access (WCDMA), the transmit power of a radio system is updated frequently (at a rate of 1500 Hz) in order to cope with fast fading. It is important to have the transmit power of a radio system set accurately. If it is set too high, then the capacity of the cell in which the radio system is camped is reduced, and if it is set too low, then the quality of the service provided to the user is compromised.
When a wireless device is transmitting using two or more radio systems, the maximum total transmit power (in milliWatts) that may be generated by that device at any particular time is equal to the sum of the maximum transmit powers (in milliWatts say) that can be generated by each of the radio systems of the device. However, it may be that the maximum total transmit power of the device is restricted or has to be limited in some way, for example to meet legal requirements or current operating conditions of the wireless device.
US-A1-2009/0275355 discloses a multi-mode wireless device that uses first and second wireless modems which operate independently over different air interfaces. When the first wireless modem is transmitting, the maximum transmit power available to the second wireless modem is reduced. When the first wireless modem ceases transmitting, the maximum transmit power available to the second wireless modem is restored. However, this is a relatively simplistic approach to the problem of controlling the total transmit power of the device.